I am writing a C programming for finding the real root, x for a cubic equation 〖ax〗^3 〖bx〗^2 cx d=0 where a≠0 and b=0.

Unfortunately, I could not output the "test case 1 & 4" (ps. sample output provided below link). Perhaps any logic syntax in my coding? Greatly appreciated if anyone could show me the correct way to do it.

 #include <iostream>
    #include <cmath>
    #include <iomanip>
        using namespace std;
    
    int main (){

    int a , b, c , d;
    double x , y;
    double interval1, interval2;
    bool stop;

    b = 0;
    x = 0;
    stop = true;

    
    cin >> a; 

 
    cin >> c;
    

    cin >> d;  
    
    interval1 = a * pow(x , 3)   b * pow(x , 2)   c * x   d;

    if (interval1 < 0){
        interval2 = interval1 *-1;
    }else{
        interval2 = interval1;
        interval1 = interval2 * -1;
    }

    while (stop=true){
        x = interval1;
        y = a * pow(x , 3)   b * pow(x , 2)   c * x   d;
    
        if(y>0 && y<0.001){
        break;
    }else {   
        if (x<interval2) { 
            interval1 = x   0.000001;
    }else{
        stop = false;
        }
    }
 }

    if (x==-0){
        x = 0;
    }

    if(a==0){
        cout << "NOT VALID" << endl;
    }else{
        std::cout << std::fixed << std::setprecision(3) << x;
  
    }
    return 0;
}

The sample output Pseudocode for the program

CodePudding user response：

Your code is almost done. You need to improve some points.

1. Change int a , b, c , d; to double a , b, c , d;

2. Change condition while (stop=true) to while (stop==true)

I tested and it works as your example.